Form: Sporadic CJD (sCJD)Cause: UnknownDistinguishing Features: Affects mainly people over the age of 60. Common symptoms include ataxia and dementia. Short course. Upon tissue examination there is spongiform change, but plaques are rarely present.

Form: Sporadic Fatal Insomnia (sFI)Cause: UnknownDistinguishing Features: Has clinical and histopathologic features indistinguishable from those of Fatal Familial Insomnia (FFI), but does not have the mutation on the prion gene that characterizes FFI.